How to study postoperative nausea and vomiting.

Anesthesiological journals are flooded by innumerable studies of postoperative nausea and vomiting (PONV). Nevertheless, PONV remains a continuing problem with an average incidence of 20-30%. This paper should provide essential information for the design, conduct, and presentation of these studies. It should also increase comparability among future studies and help clinicians in assessing and reading the literature on PONV. First, future studies should address new and relevant questions instead of repeatedly investigating prophylactically given antiemetics whose main results are predictable (e.g. already proven by meta-analysis). Second, group comparability should be based on well-proven risk factors and a simplified risk score for predicting PONV. Endless listings of doubtful risk factors should be avoided. Third, a realistic sample size estimation should be performed, i.e. in most cases at least 100 patients per group are necessary. Fourth, nausea, vomiting and rescue medication should be recorded and reported separately with the corresponding incidences (and number of patients with these separate symptoms), and the main end-point should be PONV. The entire observation period should cover 24 h. Additional reporting of the early (0-2 h) and delayed (2-24 h) postoperative period is desirable and should consider single and cumulative incidences. Lastly, interpretation of results should take into account the study hypothesis, sources of potential bias or imprecision, and the difficulties associated with multiplicity of analysis and outcomes.